As Mylenium said, without seeing your shot it's impossible to point you to anything but a general solution. That solution will most likely involve tracking skills, a fairly thorough knowledge of how the Clone tool in AE works, an understanding of basic compositing using layers, a good understanding of color correction techniques, probably some rotoscope or track matte work, and generally a very good understanding of where all of the switches and levers hidden under the hood are located and how they work. There is no one click solution for most shot cleanup work.
Here is a tutorial from my friends at Video Copilot that shows you how to put an evil alien skin on a face. Depending on your shot you may be able to use similar techniques to remove the lens flair. If your shot is anything like this one from Adobe Stock:

then it's going to take a lot more work to clean it up.
Post your shot and we can give you better advice.